In recent years, studies have been intensively carried out for a light emitting device that uses, as illumination light, fluorescence emitted from a light emitting section (wavelength converting member) which includes a fluorescent material. The light emitting section emits the fluorescence upon irradiation with excitation light which is emitted from an excitation light source. The excitation light source is a semiconductor light emitting element such as a light emitting diode (LED) and a laser diode (LD).
Patent Literature 1 discloses a lamp as an example technique related to such a light emitting device. In order to produce a high-luminance light source, the lamp disclosed in Patent Literature 1 includes a laser diode as the excitation light source. Laser beams emitted from the laser diode are coherent light: These laser beams have strong directivity, and therefore can be converged and used as the excitation light without waste. A light emitting device (hereinafter referred to as “LD light-emitting device”) including such a laser diode as the excitation light source is suitably applicable for vehicle headlamps. The use of a laser diode as an excitation light source allows production of a high-luminance light source which could not otherwise be produced with use of an LED.
In a case where such laser beams are used as excitation light, the excitation light irradiates and is thus absorbed by a minute light emitting section, that is, a light emitting section having an extremely small volume. The excitation light, however, includes a component which is not converted into fluorescence by a fluorescent material and which is instead converted into heat. Such a component easily raises a temperature of the light emitting section, and consequently impaired properties of the light emitting section or thermally damages the light emitting section.
To solve the above problem, Patent Literature 2 discloses an invention which includes a light-transmitting heat conducting member that is in a shape of a thin film and that is thermally connected to a wavelength converting member (corresponding to a light emitting section). The heat conducting member reduces heat generated by the wavelength converting member.
Patent Literature 3 discloses an invention which includes (i) a cylindrical ferrule that supports a wavelength converting member and (ii) a wire-shaped heat conducting member that is thermally connected to the ferrule. This arrangement reduces heat generated by the wavelength converting member.
Patent Literature 4 discloses an invention which includes a heat dissipating member having a passage for allowing a refrigerant to flow. The heat dissipating member is disposed at such a location as to face a surface of a light converting member (corresponding to a light emitting section) which surface is present on a side on which a semiconductor light emitting element is present. This arrangement cools the light converting member.
Patent Literature 5 discloses an arrangement of thermally connecting a light-transmitting heat sink to a surface of a high-output LED chip serving as a light source. This arrangement cools the high-output LED chip.